Understanding the effects of plastic debris on marine ecosystems is essential in encouraging decision-makers to take action. The present study investigates the effect of a 24 h experimental exposure to high density polyethylene (HDPE) microplastics (MPs) of different sizes (4–6, 11–13 and 20–25 μm) and at three concentrations (0.1, 1 and 10 mg MP.L⁻¹) on the development and locomotor activity of early stages of Pacific oyster, Crassostrea gigas. The bivalve embryo-larval assay (AFNOR, XP T90-382) was used in this study but with additional toxicity criteria: the developmental arrests, abnormal D-larvae, maximum speed and swimming trajectory. Copper (Cu), was used as a positive control. Our results show that smaller MPs (4–6 and 11–13 μm) induced higher rates of malformations and developmental arrests than the larger ones (20–25 μm). In addition, a dose-dependent decrease of maximum swimming speed was observed for larvae exposed to MPs of 4–6 and 11–13 μm. On the other hand, there was no significant difference in swimming speed with the largest MPs size tested (20–25 μm). For all three sizes of MP, there was a decrease in straight-line swimming trajectories, and an increase in circular trajectories. This abnormal swimming behaviour could affect larvae survival as well as colonization of new habitats.

了解塑料碎片对海洋生态系统的影响对于鼓励决策者采取行动至关重要。本研究调查了24小时实验暴露于三种尺寸（0.1、1和10）的不同尺寸（4–6、11–13和20–25μm）的高密度聚乙烯（HDPE）微塑料（MPs）的影响mg MP.L ^-1）对太平洋牡蛎（Crassostrea gigas）早期发育和运动能力的影响。在这项研究中使用了双壳类幼虫试验（AFNOR，XP T90-382），但还有其他毒性标准：发育停滞，D幼虫异常，最大速度和游泳轨迹。铜（Cu）用作阳性对照。我们的结果表明，较小的MP（4–6和11–13μm）比较大的MP（20–25μm）引起更高的畸形和发育停滞。另外，暴露于4-6和11-13μmMP的幼虫观察到最大游泳速度的剂量依赖性降低。另一方面，测试的最大MPs大小（20–25μm）在游泳速度上没有显着差异。对于所有三种尺寸的MP，直线游泳轨迹均减少，而圆形轨迹则有所增加。